1. Field of the Invention
The present invention relates to active matrix display devices which control thin film luminescent devices, such as electroluminescent (EL) devices emitting light by a driving current flowing in an organic semiconductive film, and light-emitting diode (LED) devices using thin film transistors (hereinafter referred to as TFTs).
2. Description of Related Art
Active matrix display devices using current-control-type luminescent devices, such as EL devices or LED devices, have been proposed. The fact that luminescent devices used in such types of display devices have self-luminescent functions provides advantages, such as obviating installation of a backlight, whereas backlights are essential for liquid crystal display devices, and providing a wider viewing angle.
FIG. 22 is a block diagram of an active matrix display device using charge-injection-type organic EL devices. In the active matrix display device 1A shown in the drawing, a plurality of scanning lines gate, a plurality of data lines sig extending in a direction perpendicular to a direction of extension of the scanning lines gate, a plurality of common feed lines com extending along the data lines sig, and a plurality of pixels 7 in a matrix formed by the data lines sig and the scanning lines gate, are formed on a transparent substrate 10.
A data line driving circuit 3 and a scanning line driving circuit 4 are provided for the data lines sig and the scanning lines gate, respectively. Each pixel 7 is provided with a conduction control circuit 50 for supplying scanning signals from a scanning line gate, and a thin film luminescent device 40 emitting based on image signals supplied from a data line sig through the conduction control circuit 50.
In this example, the conduction control circuit 50 has a first TFT 20 for supplying scanning signals from the scanning line gate to a gate electrode; a holding capacitor cap for holding image signals supplied from the data line sig through the first TFT 20; and a second TFT 30 for supplying the image signals held in the holding capacitor cap to the gate electrode. The second TFT 30 and the thin film luminescent device 40 are connected in series between an opposite electrode op (described below) and a common feed line com. The thin film luminescent device 40 emits light by a driving current from the common feed line com when the second TFT 30 is in an ON mode, and this emitting mode is maintained by a holding capacitor cap for a predetermined time.
In such a configuration of an active matrix display device 1A, as shown in FIGS. 23, 24(A), and 24(B), the first TFT 20 and the second TFT 30 are formed of islands of a semiconductive film in each pixel 7. The first TFT 20 is provided with a gate electrode 21 as a part of a scanning line gate. In the first TFT 20, one source-drain region is electrically connected to a data line sig through a contact hole in a first insulating interlayer 51, and the other region is connected to a drain electrode 22. The drain electrode 22 extends towards the region of the second TFT 30, and this extension is electrically connected to a gate electrode 31 of the second TFT 30 through a contact hole in the first insulating interlayer 51. One source-drain region of the second TFT 30 is electrically connected to a relay electrode 35 through a contact hole of the first insulating interlayer 51, and the relay electrode 35 is electrically connected to a pixel electrode 41 of the thin film luminescent device 40 through a contact hole in a second insulating interlayer 52.
Each pixel electrode 41 is independently formed in each pixel 7, as shown in FIGS. 23, 24(B), and 24(C). An organic semiconductive film 43 and an opposite electrode op are formed above the pixel electrode 41 in that order. Although the organic semiconductive film 43 is formed in each pixel 7, a stripe film may be formed over a plurality of pixels 7. The opposite electrode op is formed not only in a display section 11 including pixels 7, but also over the entire surface of the transparent substrate 10.
With reference to FIGS. 23 and 24(A) again, the other source-drain region of the second TFT 30 is electrically connected to the common feed line com through a contact hole in the first insulating interlayer 51. An extension 39 of the common feed line com faces an extension 36 of the gate electrode 31 in the second TFT 30 separated by the first insulating interlayer 51 as a dielectric film to form a holding capacitor cap.
In the active matrix display device 1A, however, only the second insulating interlayer 52 is disposed between the opposite electrode op facing the pixel electrode 41 and the data line sig on the same transparent substrate 10, which is unlike liquid crystal active matrix display devices; hence, a large capacitance is formed in the data line sig, and the data line driving circuit 3 is heavily loaded.
Accordingly, as shown in FIGS. 22, 23, 25(A), 25(B), and 25(C), the present inventors propose a reduction in parasitic capacitance in the data line sig by providing a thick insulating film (a bank layer bank; the region shaded with lines slanting downward to the left at a wide pitch) between the opposite electrode op and the data line sig. Furthermore, the present inventors propose that the region for forming the organic semiconductive film 43 be surrounded with the insulating film (bank layer bank) to block a solution discharged from an ink-jet head and to prevent bleeding of the solution towards sides in the formation of the organic semiconductive film 43.
When the entire bank layer bank is formed of a thick inorganic material in adoption of such a configuration, a problem of a prolonged film forming time arises. When the thick inorganic film is patterned, the pixel electrode 41 may be damaged due to overetching. On the other hand, when the bank layer bank is formed of an organic material, such as a resist, the organic semiconductive film 43 may deteriorate at the boundary between the organic semiconductive film 43 and the bank layer bank by the effects of the solvent components contained in the organic material in the bank layer bank.
Since formation of a thick bank layer bank causes formation of a large step difference bb, the opposite electrode op formed above the bank layer bank readily breaks on the step difference bb. Such breakage of the opposite electrode op due to the step difference bb causes insulation of the opposite electrode op from the neighboring opposite electrodes op to form point or linear defects in the display. When the opposite electrode op breaks along the outer periphery of the bank layer bank which covers the surfaces of the data line driving circuit 3 and the scanning line driving circuit 4, the opposite electrode op in the display section 11 is completely insulated from a terminal 12 and thus no image is displayed.